This is a copy of my post from another thread on the same topic:
So I've been doing some further testing. I can create a situation on my mk3 and 600 ex-rt where I can notice a much less snappy AF lock. I was not able to re-create the lag when trying to focus in a very dark (almost black) setting. Maybe, that's where I messed up in my prior testing. Maybe a completely black environment creates enough contrast between the environment and the red focus assist beam to allow focus whereas a dimly lit situation is lit just enough to give the camera trouble focusing because it can't really see the red AF assist beam as well.
I'm able to notice a significant lag when the ambient light is dim (proper exposure in camera at f/2.8, 1/50, ISO 5000).
Seems to me like I would just turn the beam OFF when I notice the ambient light is about at this level. Am I still over simplifying the issue? I get that pros need their focus to be snappy to catch those moments. Wouldn't that mean a few test shots in the environment first to gauge the settings required....including wether or not to turn the AF assist beam on/off?
Maybe I don't understand the depth of the issue because I'm not coming from a 5D mk2 where the focus is supposed to be faster. That said, I'm an engineer by trade. We are trouble shooters by nature. It seems like there's a pretty easy fix for this (just based off of what I've been able to test). If this really is an issue for a shooter, just turn the beam off when you feel like it's slowing you down. Does ambient light in a reception hall or your venues change constantly for you guys? Isn't this just a matter of your experience telling you how your camera should be set to capture moments? I'm not trying to be condescending. promise. I still don't understand what the big deal is.
